The molecular mechanisms of signal transduction in natural killer cells remains poorly understood. Recently, the zeta subunit of the TCR has been found to be present in NK cells. We have been able to demonstrate the presence of both homodimers and heterdimers of zeta on the surface of NK cells. In addition, it is clear that a fraction of zeta exists co-associated with the transmembrane form of CD16, Stimulation of NK cells with an anti-CD16 antibody results in the tyrosine phosphorylation of the zeta chain.